This invention relates to lamp reflectors, and more particularly to reflectors for optimizing the optical efficiency of a fluorescent lamp luminaire.
In a fluorescent lamp, phosphor crystals are coated on the inner surface of a glass envelope containing a mercury vapor. Electron bombardment of the vapor from a cathode generates ultraviolet light and causes the phosphor crystals to emit visible light from the surface of the coated envelope in both radial and tangential directions. Because it is generally desired that the light be directed to particular areas, reflectors are generally used to help direct the emitted light to the target areas.
A typical fluorescent lighting unit (known as a luminare), for example, has a housing known as a troffer for supporting one or more fluorescent tubular lamps and the necessary wiring and electrical hardware that provide power to the lamps. The troffer generally has a box-like structure often used as a reflector with the light rays incident on the side and rear portions of the troffer being either absorbed or reflected by the surface. The inner surfaces of the troffer are typically painted white in order to decrease the amount of light absorbed by the surfaces. In those regions where the lamp is relatively close to the troffer, particularly where the troffer surface is directly behind the lamp, a significant portion of the light rays are either reflected back into the lamp or indirectly guided to the illuminated area by making multiple light scattering reflections along the walls of the troffer before exiting the troffer.
With rising energy costs, efforts are being made to improve the optical efficiency of lamp reflectors for lighting fixtures. The optical efficiency of a reflector represents the total amount of light directed to an area relative to the total amount of light generated by the lamp.
Reflector materials used for the reflection of fluorescent light are fabricated by laminating metal films onto metal support sheets. One approach for providing such a reflector material includes applying an adhesive layer onto an extruded polymer substrate sheet that is sufficiently thick to support the subsequently deposited polymer and metal films. Prior to applying the adhesive, the metal support sheet is often provided with a passivation layer to protect the surface of the metal support sheet from contamination, and an additional protective film is then applied over the adhesive layer. A metal film is vapor deposited over the polymer film followed by anti-tarnish, UV absorber, and abrasion resistance coatings. A polymer film is then bonded onto the metal film with a front cover film deposited over the polymer to protect the reflector material during shipment and handling. The metal film has mirror-like qualities, known as specular metals, such as silver or aluminum. The metal film is typically vacuum metallized onto the polymer film.
The abrasion resistant layer often includes the ultraviolet light absorber for screening ultraviolet light from the adhesive layer and polymer film. Ultraviolet light over long periods of time can cause degradation and molecular breakdown within the polymer film causing the film to "yellow". This breakdown of the polymer results in a reduction in the specularity of the reflector material. The reflector material is fabricated into a lamp reflector by first cutting the laminated sheets to desired dimensions and cutting or punching lamp clearance holes in the laminated film. A press is then used to shape the reflector material with a series of bends providing a concave shaped member having a number of reflective facets. The sheet of reflector material is shaped with the press by marking locations of each bend, carefully placing the marked positions along the bending element of the press, and bringing the press arm down to crease the sheet with an appropriate amount of force. This operation is repeated until the multi-faceted reflector is completed. The fabrication of some multi-faceted reflectors may involve well over thirty bend operations. The reflector is then ready to be mounted within the light fixture along with lamp brackets and other hardware.